The invention relates to the positive effect on feed utilisation after supplementation of feed or food with given non-starch polysaccharides (NSP). NSP include a range of compounds possessing different physicochemical properties. Arabinoxylans are an important group of cereal NSP and are also referred to as pentosans, which consist of a main chain of beta-1,4-linked D-xylopyranosyl units to which O-2 and/or O-3 L-arabinofuranosyl units are linked. In a typical arabinoxylan unsubstituted, monosubstituted and disubstituted xylose residues occur (see FIG. 1). Arabinoxylans are either water-extractable or water-unextractable. The latter can be partially solubilised under alkaline conditions or by using enzymes and bind large amounts of water. The water-extractable arabinoxylans have an extraordinary viscosity forming potential. In general, their molecular masses are very high (up to 800,000 Dalton) depending on the source and extraction method. Despite the fact that they are only minor constituents, they are important for the functionality of cereals in biotechnological processes such as the production of wheat starch, pasta and beer, breadmaking and feed applications.
More in general, the nutritional effects of NSP in monogastric animals are diverse and, in some cases, extreme. It is, however, generally conceded that the major detrimental effects of NSP are associated with the viscous nature of these polysaccharides, their physiological and morphological effects on the digestive tract and the interaction with the microflora of the gut. The mechanisms include altered intestinal transit time, modification of the intestinal mucosa, and changes in hormonal regulation due to a varied rate of nutrient absorption (Vahouny 1982). The viscous properties of NSP and more particularly those of the high molecular mass, water extractable NSP, are a major factor in the anti-nutritive effect of NSP in monogastric diets.
This is illustrated by the findings of Choct and Annison (1992a) demonstrating that the concentration of waterextractable arabinoxylan in broiler diets is positively correlated with the relative depression in metabolisable energy, nitrogen retention, feed-conversion efficiency, and weight gain. Wheat diets containing 4% arabinoxylans decreased digestibility of starch, protein, and lipids by 14.6, 18.7, and 25.8%, respectively. Differences in content and composition of NSPs among barley or wheat varieties are associated with differential effects of these cereals on poultry productivity. Barley varieties can e.g. be classified as having a “high” or “low” contents of β-glucan, which is responsible for significant differences in biological responses when barley-based diets are fed to poultry (Campbell et al. 1989).
Adding microbial enzymes to wheat- and barley-based monogastric animal feeds to hydrolyze NSPs and reduce the negative effects of antinutritive factors, minimize variability, and therefore, improve ingredient value is now a commonplace practice. Indeed, while hydrolysis of arabinoxylan is facilitated by several types of endo- and exo-acting enzymes, the 1,4-β-D-xylanhydrolase, hereafter referred to as endo-xylanase (EC 3.2.1.8) clearly has a key role in the process, hence its use in many biotechnological processes in which cereals are used, such as in feed production.
However, the use of microbial enzymes in food and feed processing is based on empirism rather than on sound scientific insights. To be efficient it is often desirable that the enzymes are sufficiently impure to have other side effects so that they can act in synergy (Zyla et al 1999). On the other hand, enzymic degradation of feed arabinoxylans may as well create adverse effects that sometimes are greater than the effect of the original polymer (Zyla et al 1999). Dietary supplementation with enzymes which degrade xylans, arabinose and mannans, may e.g. generate degradation products that cause metabolic problems (Carre et al, 195; Iji, 1999; Naveed, 1999; Zyla et al, 1999a,b) or other adverse advents may occur due to the absorption and subsequent excretion of the monomers, and other compounds such as fatty acids (Savory 1992a, b, Care et al, 1995; Gdala et al, 1997; Zdunczyk et al, 1998, Kocher et al 1999).
The positive effect of the addition of NSP hydrolysing enzymes is mainly explained by the fact that anti-nutritive activity of NSP, such as the high viscosity of the digesta, is largely eliminated when the NSP polymers are cleaved into smaller fragments. However, it is largely unknown whether the degraded NSP fragments have any positive effect per se on the feed utilisation and growth performance of monogastric animals. It is generally accepted that part of rapidly fermentable oligosaccharides, such as those obtained after (enzymatic) fragmentation of the NSP, promote the growth of beneficial microflora in the gut, which is expected to lead to better health in pigs (Choct and Kocher, 2000). In poultry the role of dietary oligosaccharides is not clear. Although a prebiotic effect was described for some types of oligosaccharides (Spring et al., 2000), other authors argued that the presence of oligosaccharides in poultry diets increases fluid retention, hydrogen production and diarhea, leading to an impaired utilisation of nutrients (Saini et al., 1989, Coon et al., 1990). Therefore, Choct and Kocher (2000) concluded it is difficult to say whether oligosaccharides are “nutrients” or “anti-nutrients”. They attributed this uncertainty to the tremendous diversity of NSP-oligosaccharides that can potentially be derived from vegetable material. This diversity is also observed for the arabinoxylan oligosaccharides. In first instance the diversity is related to the source of the arabinoxylans. For example the arabinoxylan population in rice exhibits a very high degree of branching, indeed the ratio arabinose over xylose is about 1 in rice (Shibuya et al., 1985) while this is significantly lower in rye and wheat arabinoxylan (ratio arabinose over xylose ca. 0.5) (Maes et al., 1985). This difference in the degree of branching will influence both the efficiency of enzymatic fragmentation of the arabinoxylans as well as the nature and length of the obtained arabino-oligosaccharides. Furthermore, the nature of the fragmented arabinoxylans is determined by the fragmentation process applied. Depending on the applied process (enzymatic hydrolysis, acid hydrolysis, alkalic pretreatment) and the process parameters used (time, temperature, concentration of the arabinoxylan, concentration of the enzyme, pH, type of enzyme) different fragmentation products will be obtained, which differ in molecular weight, arabinose/xylose ratio, substitution pattern and ferulinic acid content.